Development of a physically-based catchment-scale rainfall-runoff model using the vertical quasi-two-dimensional surface-subsurface flow modeling

In this study, we developed a catchment-scale rainfall-runoff model using the vertical quasi-two-dimensional surface-subsurface flow model (quasi-2D model) and applied it to the upstream catchment of the Kamo River in Japan. The modeling of slope connections was devised to enhance computational stability, and the settings of computational cell sizes were designed according to the slope angles to reduce the computational cost while maintaining accuracy. Rainfall-runoff simulations were conducted for several floods, and the model was validated by comparing it to observational data. The quasi-2D model generally reproduced the observed river discharge well; however, it tended to overestimate the peak discharge. The present model seemed to generate excessive surface flows in mountainous areas, suggesting the need to incorporate various flow pathways, such as macropores in the soil and groundwater flows, which enhance the underground drainage capacity. The simulations for an area of 138.1 km2 required less than one-tenth of the actual time, partly because of the parallel computation of two independent catchments.